This invention relates to an interactive visual display communications system and more particularly to a visual communications system using narrow bandwidth communication links between the system terminals in which the common graphic picture on the terminal displays is generated or modified by any one of the terminals.
Present interactive visual display communications systems embody one of two configurations: a central computer connected to many non-intelligent terminals or a distributed system with a number of equally capable nodes connected together. The former arrangement is an extension of the conventional time-shared computing facility where cost is minimized by placing most of the computing resources at a central facility and a minimum of capability at the terminal. However, difficulty arises because of low transmission speeds and poor time-shared response. Some of the difficulty may be alleviated by providing local processing power in the terminal but this arrangement too has its own problems such as delineating the components to be placed in the terminal and that of passing information between the terminal and the central processor.
In the past, the greatest incentive for a time-shared arrangement, or a modification thereof, was the relatively high cost of processing power, memory and related computer components. With the present lower costs, and the prospects for even further decreases in the future, cost of computer components is no longer as much of a determining factor. But the cost of communication links is still unresolved, particularly if the amount of data to be transmitted is large.
On the other hand, present narrow-bandwidth visual communications systems may consist of a telewriter system, a facsimile system or a slow-scan televideo system. Of these only the telewriter systems are interactive because long delays are incurred in the use of facsimile or slow-scan television frames.
There are both mechanical and electronic telewriter systems. Mechanical telewriters use a telephone line to link two motor controlled styli and require all visual material to be traced on the sender's platen. Essentially, these machines only allow hand drawings to be simultaneously traced at a distance. Electronic telewriters forego the mechanical problems of the styli, motors and paper by outputting on a television-like display screen. Additional features such as colour, intensity and the automatic retrieval of previously generated visual images are possible, but in general these devices only reproduce simple drawings at a distance. In addition, telewriter systems do not provide a capability of interacting with the structure of the visual material. Visual data can only be handled on a line basis so that sub-sections of a picture cannot be automatically replicated or otherwise manipulated.